Piezoelectric type switching relay



May 31, 1949. w.-P. MASON 2,471,967

PIEZOELECTRIC TYPE SWITCHING RELAY Filed May 3, 1946 FIG.

I I I P/EZOELE C TR/C MATERIAL INVENTOR w P. MASON ATTORNEY Patented May 31, 1949 PIEZOELECTRIC TYPE SWITCHING RELAY Warren P. Mason, West Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 3, 1946, Serial No. 667,071

This invention relates to improvements in the construction of electrical relays and more particularly to the improvement of relays which depend for their operation on the deformation of piezoelectric crystals when electromotive forces are applied thereto.

An object of this invention is the improvement of relays by providing a relay structure which is responsive in the greatest degree to relatively small amounts of electric power.

A further object of this invention is the improvement of piezoelectric crystal relays by in creasing their responsiveness to small amounts of electric power.

A further object is the provision of a piezoelectric relay the component parts of which have been designed to provide large deformation in response to small power and to greatly increase the motion derived from the deformation of piezoelectric crystals when electromotive force is applied to the crystal elements.

It has long been known that when an electromotive force is applied to a piezoelectric crystal, the crystal undergoes a deformation. Advantage has been taken of this deformation of the crystal in the design of relays, the motion of the switching elements of which has been controlled through the deformation of the crystals when voltage is applied. An inherent difli-culty limiting the wider application of crystal relays, particularly in the communication switching plant, is

the relatively small deformation resulting from the application of the elcctromotive force, particularly electromotive force of the magnitude used in communication switching plants.

The deflections obtainable by means of piezoelectric crystals have been increased through a choice of crystals of particular composition, as well as by a choice of the position of the cutting of plates or sections of the crystal with respect to the various axes of the crystal and also by the assembly of two individual plates or sections of a crystal into a unit assembly known as a double strip crystal unit.

While various piezoelectric materials differing widely as to their piezoelectric constants and properties may be employed as the crystal elements in carrying out my invention, I prefer to employ crystalline ammonium dihydrogen phosphate, NH4H2PO4 known in the art and hereinafter referred to as ADP crystals. But it is to be understood that other materials, such as potassium dihydrogen phosphate, KH2PO4, ammonium dihydrogen arsenate, NH4H2ASO4, potassium dihydrogen arsenate, KHLASOII, as well as iso- 5 Claims. (Cl. 171-327) morphous combinations of the four foregoing materials and other materials including Rochelle salt crystals may be employed.

Four 45-degree Z-cut crystal plates or sections are employed in carrying out the present invention. These four crystal plates are assembled in pairs to form two double strip units. Double strip units may be formed of two crystal plates or sections cemented together along an opposing broad surface of each plate and are well known in the art, being described for instance in Patent 1,781,- 680, Walter G. Cady, November 18, 1930. A conducting coating of evaporated gold or other conducting metal may be applied to the broad external surfaces of each of the crystal plates forming each double strip unit in the manner described in Patent 2,241,228, H. W. Weinhart, May 6, 1941. A thin copper foil terminal is attached to each of the two exterior conducting surfaces of the unit. The two double strip units, one slightly longer than the other, are disposed in opposed spaced relation. The double strip units are each fixed in position in a base at one corresponding end. Each double strip unit is free to flex along its length. The polarity of the double strip units and the potential applied across each of the units, between the external conducting surfaces, are arranged so that the two double strip units are flexed each toward the other or away from the other simultaneously. To this end one of the units is reversed with respect to the other and with respect to the applied voltages so that this occurs. The sum of the displacements caused by the double strip units is multiplied by a lever mechanism attached to the free ends of the two double strip units, which lever serves as the armature of the relay. The lever armature is pivoted at the end of the longer of the two double strip units. One end of the lever armature is attached to the shorter of the two double strip units in relatively closely spaced relationship with the pivot or fulcrum, so that the length of the lever armature arm between the two ends of the double strip unit is relatively short compared to the length of the lever armature arm between the pivot and the free end of the lever armature, to which free end the electrical contacts are attached. The increased displacement of the contact carrying end of the lever armature is effected by a number of factors as follows:

1. The material of the crystal. ADP crystals, because of the large magnitude of their deformation in response to relatively low applied potentials as well as their relative stability and other desirable characteristics are recommended.

2. The position of the cut of the crystal plates or sections relative to the various crystal axes. In the case of ADP and the other three dihydrogen-type crystals mentioned in the foregoing, it is recommended that each of the four individual plates or sections required to form the two double strip units be cut so that its opposing broad surfaces are both perpendicular to the Z axis of the virgin crystal and so that the broad surfaces are parallel and so that the linear axis of the crystal plate section be at 45 degrees to both the a.- and y axis of the virgin crystal. Such crystal plates are known in the art as 45 degrees Z-cut plates.

3. The assembly of two unit crystal plates into a double strip unit.

4. The relative displacement of the two double strip units.

5. The control of the armature lever through the two relatively displaceable double strip units.

Piezoelectric relay structures formed of a single double strip unit and operating circuits suitable for such relays are well known in the art. For instance, they are disclosed in my United States Patent 2,166,763, granted July 18, 193 0, for Piezoelectric apparatus. Piezoelectric relays may be characterized as electrostatic in that they are essentially capacity elements and they operate in response to a charge impressed upon their input terminals. They remain operated without further application of energy to the relay until such charge has been Withdrawn or such an interval has elapsed that the charge has dissipated. Such relays present many desirable features. Finite amounts of power are required to operate them but no power is required to hold them in an operated position. They may, moreover, be operated with moderate electromotive forces over circuits of extremely high impedance ranging in some cases in the order of megohms. This enables the armature and contact movements sufiiciently large so that they can be effectively employed for the usual switching functions. The structure of the present invention provides larger armature displacement than has heretofore been possible with relays of the piezoelectric type increasing the field of application of this type of relay with its highly advantageous low power consumption characteristics.

Additional aspects and features of the invention will be apparent from a consideration of the appended claims and the detailed specification taken in connection with the accompanying drawing which discloses a preferred embodiment of the invention.

In the drawing,

Fig. 1 is a plan view partly in section of the relay of the present invention, and

Fig. 2 is an enlarged cross-section taken on the plane 2--2 of Fig. 1.

Refer now to Figs. 1 and 2. A fiat circular base plate I, preferably of cold rolled steel, is arranged with an annular mounting flange 2 and is provided with mounting apertures 3 and an axial contact aperture 4. Secured to the plate 2 by means of screws and in axial alignment therewith is 4 an insulating disc 6, which may be of hard rubber, or other suitable insulating material, and having a circular section of somewhat smaller diameter than the diameter of the main section of base plate 2. The mounting is apertured to receive the screws 5 which engage tapped holes in the base plate I. The disc 6 is counter-bored so that the heads of the screws 5 may be depressed below the top surface of the disc. The insulating disc 6 is apertured at 'I and 8 to accommodate the two double strip units 9 and Ill which are cemented in the apertures. An axial opening in the bottom of insulating disc 6 is provided through which copper foil conductors II and I2 may be introduced for connection with the double strip units. The conductor I I is connected to the conducting surfaces on the right and conductor I2 to the conducting surfaces on the left of each of double strip units 9 and I0 preferably by soldering the copper foil connections to the conducting surfaces of the double strip units. The double strip unit 9 is longer than the double strip unit I0. Secured to the free end of the double strip units 9 and I0, preferably by cementing, and insulated therefrom by means of insulating elements 40 and M connected to the double strip units are the armature actuating elements I3 and I4, which may be of cold rolled steel and arranged for instance as stirrup or U-shaped elements, the opposing arms of each of which have. aligned apertures near their extremities to accommodate a lever pivot pin, such as I! in each stirrup. The

armature I8 at its lower end, as seen in the draw-.

ing, has two arms folded inwardly to form a U- shaped section. Each of these two lower armature arms has two apertures aligned in pairs and in alignment with the corresponding apertures in the two stirrup elements, through which the armature pivot pins may pass and about each of which pivot pins the armature is rotatable in a limited arc. The major axis @of each pivot pin, such as H, is in alignmentlongitudinally with the upper portion of the armature I8 which has a bent section I9 to provide sufficient displacement of the lower U-shaped armature portion to accommodate the pivot pins in the aligned position. A pair of contacts 20 and 2| are secured in any convenient manner, such as by welding, to the opposed broad surfaces of the armatures I8 near the upper free end thereof. An armature conductor 22 has a portion intermediate its ends and near its lower protruding extremity secured in the insulating disc 6. A very flexible conducting spring 23 connects the upper end of the arma ture conductor 22 with the lower portion of the armature I8. The connection to the armature may be made on the top surface of the armature at 24 midway between the pivot points by soldering or in any convenient manner. A pair of bent contact springs 25 and 26 having individual contacts 21 and 28 secured thereto adjacent their upper ends, in a position to engage contacts 20 and 2 I, respectively, are secured near their lowerextremities in spring insulating mounting assemblies 29 and 3!] by means of screws, which engage tapped holes in cylindrical dust cover 3I. Dust cover 3| has an enlarged cylindrical section 32 near its base to fit snugly about the upper peripheral surface of base plate I to which it may be secured by screws 33 which pass through apertures in the enlarged section 32 to engage tapped holes in base plate I. A cylindrical cap 34 fits over the top end of dust cover 3| with a spring fit and its lower edge abuts against the annular stop ring 42 formed in dust cover 3|.

Contact spring conductors 35 and 36 are soldered to contact springs 25 and 26, respectively, and are secured intermediate their ends and near their lower extremities in insulating disc 6. Contact spring conductor 35, double strip conductor l2 and armature conductor 22 are each connected preferably by soldering to an individually insulated contact which contacts are secured to insulating disc 6 by means of screw 31. Double strip unit conductor 9 and contact spring conductor 36 are similarly arranged and secured to insulating disc 6 by means of screw 38.

The operation of the relay is controlled by impressing a potential of a first polarity between conductors H and I2 to flex the double strip units each toward the other and reversing the polarity to flex the units each away from the other. The application of the potential may be controlled by any desired reversible switching means, not shown, connected to conductors H and I 2. When the double strip units approach one another the armature pivot connected to double strip unit 9 will be actuated toward the left. Simultaneously the lower end of the lever of armature l8 will be actuated to the right by the movement of double strip unit [0, thus rotating the upper end of armature [8 toward the left, or counter-clockwise, to close contacts 20 and 21. When the polarity of the potential applied to the double strip unit is reversed, the pivot controlled by double strip unit 9 will be moved toward the right and the lower end of armature I8 will be moved toward the left rotating the upper end of armature I8 toward the right, or clockwise, to close contacts 2! and 28. When contacts 20 and 21 are closed a circuit is established between the incoming conductor connected to armature conductor 22 and the incoming conductor connected to spring conductor 35 through armature I8 and contact spring 25. When contacts 2| and 28 are closed a circuit is established between the incoming conductor connected to armature conductor 22 and the incoming conductor connected to spring conductor 36 through armature l8 and contact spring 26. The power required for either of these operations is relatively small. The power required to maintain either circuit closed is practically negligible.

Following is a computation of the displacement obtainable using two double strip units each assembled from two 45-degree Z-cut ADP crystal plates. The piezoelectric constant of ADP (ratio of expansion per unit of length to applied potential gradient, in c. g. s. units) is '75 10- Hence the expansion for unit length is Al V T 75 X where AZ is the change in length, l is the length and t the thickness of the individual crystal plate in centimeters and V the voltage.

For a crystal 3 inches or 7.62 centimeters long and 0.1 centimeter thick 1.9X 10- centimeters If two such crystals are glued together to provide a single double strip unit clamped at one end it has been demonstrated that the displacement is increased in the ratio 3/t1, where t1 is now the total thickness of the double strip unit which is twice the thickness of a single unit. displacement will be 1.9x1o 114.2=2.17 1o .00217 cm.=.85 mil for volts With two double strip units actuating the lever armature and in which th ratio of the longer to the shorter arm of the lever is 10 to 1 and in which the pivot is displaced as in the arrangement described in the foregoing the actual displacement of the free end of the armature would be .85 20=17 mils for 100 volts direct current applied to the relay.

The two double strip units in such a relay as described would have a capacity of 835 micromicrofarads and a leakage resistance of 13 megohms for crystal plates presently obtainable. It would, therefore, take 4=.1'( 10- joules to charge up and a steady power of .7 10 watts to hold the relay operated. As the quality of the crystals is improved the power required would be reduced.

It is particularly pointed out that the invention may be incorporated in many different embodiments and is not limited to the particular embodiment described herein. For instance the connections between the two double strip units and the armature lever may be interchanged and many other changes may be effected in the relationship of the various elements without departing from the spirit and scope of the invention which is defined in the appended claims.

What is claimed is:

1. In an electrical system, a relay, a plurality of double strip crystal units in said relay, said units of difierent lengths, a linkage and an armature cooperatively controlled by said units through said linkage, so as to amplify the motion of said armature.

2. In an electrical system, a relay, a plurality of double strip crystal units of unequal lengths, interconnected through a linkage in said relay and a lever type armature controlled through said linkage, by the combined motions of said units.

3. In an electrical system, a relay, a first and a second double strip crystal in said relay, said second unit longer than said first unit and a lever type armature having a pivot connected to said second unit and an arm connected to said first unit.

4. In an electrical system, a relay, two double strip crystal units therein, said units of different lengths and a lever type armature linked to said unitsand cooperatively controlled by the displacement of said units.

5. In an electrical system, a relay, two double strip crystal units therein, said units of unequal lengths, a. lever type armature therein, a first connection between a displaceable end of one of said units and an end of said armature, and a second connection between a displaceable end of the other of said units and said armature at a position intermediate the ends of said armature.

WARREN P. MASON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Heam Dec, 5, 1939 Hence the =1l4.2 or will be Number 

